Promo code not app****, full amount deducted

I ordered on their app with a promo code, and it was not my first time ordering online. promo-code got app**** and i was told i will pay a less amount, to my surprise when the amount was deducted from my account, the full amount was deducted and not what i saw at checkout. i contacted ubereats on facebook they said they saw the code was app****, a few days later they contact me again and say i did not apply the promo i had probably thought i had. Their statements dont make sense to me at all.